The present invention relates generally to semiconductor devices, and more particularly to a lead frame having a grooved tip for securing a bond wire to the tip.
Wire bonding technology is used for connecting bond wires between a semiconductor die and lead fingers of a lead frame or substrate electrical connection pads. The wire bonding process includes feeding the bond wire through a capillary of a wire bonding device and using the capillary to facilitate the bonding of the wire to the die and the lead frame or substrate.
FIG. 1 is a cross-sectional view of a conventional semiconductor device 10 having a semiconductor die 12, a lead frame 14 having a die flag 16 and lead fingers 18 surrounding the die flag 16, bond wires 20 extending between the die 12 and the lead fingers 18, and a molding compound 22 that encapsulates the semiconductor die 12 and bond wires 20.
In the assembly process, the bond wires 20 are attached and electrically connected to bond pads of the die and ends of the lead fingers (or substrate) with a wire bonding machine by applying ultrasonic pressure and heat. For example, a bond wire is threaded through a capillary and then a free end of the bond wire is first melted to form a free air ball (FAB). The FAB is attached to the die bond pad by pressing the FAB against a die bond pad and applying thermal and ultrasonic energy. The bond wire 20 is then moved to the surface of a respective lead finger 18 of the lead frame 14 using the wire bonding device and then pressed onto the surface of the lead finger 18 again by applying ultrasonic and thermal energy. Once the wire 20 is attached to the lead finger 18, the capillary pulls on and breaks the wire 20 from the lead finger 18 and then the process is repeated with the capillary going from die bond pad to lead finger.
FIG. 2 is an illustration of the bond wire 20 being attached to a lead finger or the lead frame 14 with a capillary 30. This bond usually is called a stitch bond 32. The bond to the die bond pad sometimes is referred to as the first bond and the bond to the lead finger as the second bond. One problem in semiconductor device assembly is a poor second bond. That is, a stitch bond generally is not as reliable as a ball bond. For example, For example, the second bond
FIGS. 3, 4 and 5 are photographs of poor or compromised second bonds. FIG. 3 is a picture 40 of a broken stitch bond 42 that was damaged when the substrate was subjected to an open/short failure test. FIG. 4 is a picture 44 of a broken stitch bond 46 that was damaged in a similar manner. FIG. 5 is a picture 48 of two stitch bonds 50 and 52 having heel cracks.
Accordingly, it would be advantageous to be able to form a more reliable second bond and have a semiconductor device with more reliable second bonds.